1. Field of the Invention
The present invention relates to an electronic endoscope having a video-scope and a video-processor, and especially relates to the transmission of digital video signals.
2. Description of the Related Art
In a conventional electronic endoscope, an image sensor, such as a CCD, is provided at a distal end of a video-scope, and an object image is formed on the image sensor when the video-scope is inserted into a body-cavity. In a video-processor, image-pixel signals, read from the image sensor, are subjected to various processes so that video signals corresponding to the object image are generated. The video signals are fed to a TV monitor, thus the object image, such as the inner wall of a stomach, is displayed on the monitor. Recently, not only analog video signals but also digital video signals can be transmitted from the video-processor to the monitor and other peripheral apparatus including a video recorder. As there is less degradation of the digital video signals during transmission compared to the analog video signals, an object image of better quality can be displayed on the monitor.
Normally, the digital video signals are generated and processed in accordance with a color TV standard, such as NTSC. A display unit and a video recorder corresponding to the color TV standard are used with the electronic endoscope. On the other hand, in the medical field, computer systems have recently been utilized for filing of the observed image, patient""s list and so on. However, processing of the digital video signal for the computer system is different from the TV standard. Therefore, when using a display and a filing system for a computer, the degradation of the video signals occurs in the process of transmission, and the picture quality decreases.
Therefore, an object of the present invention is to provide an electronic endoscope system capable of transmitting digital video signals to the computer system, while limiting the degradation of picture quality.
An electronic endoscope according to the present invention has a video-processor and a video-scope. The video-scope has an image sensor, and is detachably connected to the video-processor. A computer is also connected to the video-processor. An object image is formed on the image sensor, thus image-pixel signals corresponding to the object image a regenerated. The image-pixel signals are read from the image sensor, and the video-processor processes the image-pixel signals to obtain video signals. The video-processor has a video signal processor and a first pulse generator. The video signal processor generates digital video signals on the basis of the image-pixel signals and outputs the signals to the computer. The first pulse generator for the video signal processor feeds clock pulses to the video signal processor in accordance with a sampling frequency, such that the digital video signals are generated and output to the computer in accordance with the sampling frequency. The sampling frequency corresponds to a square-pixel frequency for the computer.
For digital processing of video signals, the sampling frequency for a computer is different to the sampling frequency for a digital TV standard. According to the present invention, digital video signals are generated and output to the computer in accordance with a square-pixel frequency corresponding to a computer video standard. Therefore, when transmitting the digital video signals to the computer and processing the signals in the computer, adverse degradation of the video signals does not substantially occur during the digital processing. Consequently, picture quality is maintained. When the TV standard is a NTSC standard, applied in America and Japan and so on, the square-pixel frequency is 12.2727 MHz. Where the PAL standard is applied, in Europe, Australia and so on, the square-pixel frequency is 14.75 MHz.
Preferably, the sampling frequency to the video signal processor is set to xe2x80x9cnxe2x80x9d times the square-pixel frequency or xe2x80x9c1/nxe2x80x9d times the square-pixel frequency. Herein, xe2x80x9cnxe2x80x9d represents integers.
Preferably, a digital recorder for recording the object image as digital image data is connected to the computer, and a display unit, for displaying the object image, is also connected. Note that, the display unit corresponds to a computer video standard, such as the VGA standard and the digital image data is recorded in the digital recorder, such as a CD-R (Compact Disc-Recordable) in accordance with the square pixel frequency. When the digital video signals are fed to the display unit and the digital recorder, the object image with high picture quality is displayed on the display unit, and is recorded by the digital recorder if required.
For color image photographing, as an example, a R, G, B sequential method is applied. Thus, the image-pixel signals are transformed to digital R, G, B signals, which correspond to red color, green and blue color respectively. Preferably, the video signal processor has a matrix circuit and a multiplexer. The matrix circuit transforms the digital R, G, B signals to digital luminance signals and digital color difference signals. The multiplexer processes the digital luminance signals and the digital color difference signals. Consequently, multiplexed digital video signals are generated as the digital video signals. Thus, the multiple digital video signals are transmitted between networked computer apparatus via a LAN (Local Area Network), i.e., an Ethernet.
Preferably, the multiplexer generates the multiple digital video signals such that a ratio of the sampling frequency of the digital luminance signals and the sampling frequency of the digital color difference signals in the multiplexed digital video signals becomes xe2x80x9c4:2:2xe2x80x9d. This ratio depends upon a ratio of the digital TV standard. For example, the clock frequency of clock pulses fed to the matrix circuit is the same as the square-pixel frequency, and the clock frequency of clock pulses fed to the multiplexer is two times the square-pixel frequency.
Preferably, the video signal processor further includes a parallel/serial converter. The parallel/serial converter transforms the multiple digital video signals, which are digital parallel video signals, to digital serial video signals to send to the computer. Note that, the first pulse generator feeds the clock pulses to the parallel/serial converter in accordance with the square-pixel frequency. As the digital serial video signals are transmitted, a low cost cable for serial transmission compared to a cable for parallel transmission can be used. Namely, a hardware cost saving is achieved.
Preferably, A decoder is provided between the video-processor and the computer for feeding the digital R, G, B signals to the computer. The decoder has a serial/parallel converter, demultiplexer, an inverse matrix circuit and a second pulse generator. The serial/parallel converter transforms the digital serial video signals to multiple digital video signals. The demultiplexer processes the multiple digital video signals to restore the digital luminance signals and the digital color difference signals. The inverse matrix circuit transforms the digital luminance signals and the digital color difference signals to digital R, G, B signals. The second pulse generator for the decoder feeds clock pulses to the serial/parallel converter, the demultiplexer and the inverse matrix circuit, in accordance with the square-pixel frequency.